Legacy waveforms on Software Defined Radio: Can hierarchical modulation offer an added value to SDR operators?

Military tactical communications is taking the next step in its evolution. Many nations spend considerable efforts to bring the novel Software Defined Radio (SDR) technology into service. SDRs allow military radio operators to change waveforms on-the-fly according to the mission needs. New capabilities can be loaded as so-called Waveform Application (WFA). Before novel waveforms with wideband networking capabilities will be available in the future, most nations have launched projects to port legacy waveforms to SDRs. These WFAs on the modern SDRs shall ensure interoperable communication to legacy radios in situations where both types of radio equipment are deployed at the same time in the same mission. In this paper, we present first results of our analysis if an added value can be provided to the operators at SDRs, e.g., in terms of a higher data throughput or robustness. As an example, we apply the concept of hierarchical modulations to a legacy waveform. The modulation scheme of the legacy waveform acts as the base-layer which ensures the over-the-air interoperability to legacy radios. Additional information can be transmitted between SDRs only utilizing some extra enhancement-layers.